Chemistry Notes II

Oxidation of alcoholsAlcohols are oxidised with acidified dichromate ions (Cr2O72)This mixture can be made from potassium dichromate and sulphuric acid. (K2CrO7)During the reaction, the acidified potassium dichromate changes colour from orange to green.Primary alcoholsPrimary alcohols are oxidised to aldehydes and then carboxylic acids and waterFor carboxylic acid, refluxFor aldehyde, distilSecondary alcoholsOxidised to ketones only. Reactions of aldehydes and ketonesAldehydes and ketones can be reduced to alcohols by using warm NaBH4Nucleophillic additionReact with NaBH3BH4 acts as source of hydride ionsSee Figure 6 in book Carboxylic acidsFunctional group ­COOHCarboxylic acids with less than 4 carbons are very soluble in water. The highly polar C=O and OHbonds allow carboxylic acid molecules to form hydrogen bonds with water molecules. As thenumber of carbons increases, the solubility decreases.Carboxylic acids are relatively weak.

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Carbonyl Compound TestsAldehydes and ketones can be detected using 2, 4dinitrophenylhydraxine (2, 4DNP)A solution of 2, 4DNP with methanol and sulphuric acid is known as Brady's reagent.If an aldehyde or ketone is present then the solution will turn yellow or orange.Only works for aldehyde and ketones.Tollen's reagent is a weak oxidising agent used to distinguish between aldehydes and ketones.Aldehydes are easily oxidised to carboxylic acids by Tollen's reagent. Ketones are not.…read more

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Triglycerides and health Fats and oils come from saturated or unsaturated fatty acids Foods high in saturated fats are bad for you ­ increased risk of heart disease by raising blood cholesterol levels. Unsaturated fats were presumed to be healthy but they can exist in two states: cis and Trans isomers.Cis groups on same sideTrans Groups on opposite sides. In nature, fatty acids exist in the cis form.…read more

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Ethyl/methyl ester of a fatty acid. Made by transesterification.React triglycerides with methanol/ethanol with sodium/potassium hydroxide. Triglycerides Fats and oils are esters of long chain carboxylic acids called fatty acids. Fats are solid and oils are liquid. Triglycerides are triesters of glycerol (propane1, 2, 3triol) and 3 fatty acids joined to each of the alcohol groups through an ester linkage. Fatty acids can be saturated or unsaturated. Most natural fatty acids have an even number of carbons.…read more

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EstersEsterificationEsterification is the reaction of an alcohol with a carboxylic acid to produce an ester and water.Esters can be made by reacting a carboxylic acid with an alcohol in the presence of an acid catalyst(Sulphuric acid)See diagram in bookEsters can also be prepared by heating an acid anhydride with an alcohol.See diagram in bookAn acid anhydride is formed by the removal of water from two carboxylic acid molecules.…read more

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PolymerisationAddition polymerisationAll the atoms in the monomer are used. Made from a monomer with C=C bond.Condensation PolymerisationMonomers join up with the expulsion of small molecules. Not all the original atoms are present in thepolymer. Can be made from monomers with 2 different functional groups.…read more

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PolyamidesIn a polyamide, the monomers have a carboxyl group, COOH and an amine group, NH2Polyamides can be made from two different monomers a carboxylic acid monomer and an aminemonomer, or they can be made from one type of monomer with both functional groups(polypeptides and proteins).During polymerisation: A bond forms between an amine group and a carboxyl group An amide link forms and water is eliminated.…read more